The Movement of Earth’s Poles Led to the Current “Ice Age”

December 5, 2018

Earth shifted away from its spin axis in the last 12 million years.

Geophysicists from the Rice University analyzed the evidence from the Pacific Ocean to determine that the Earth has made a slight shift relative to its spin axis within the past 12 million years. The study published in the journal ‘Geophysical Research Letters’ also mentioned that the ice age, which began around 3.2 million years ago, was initiated by this shift as it pushed Greenland towards the North Pole.

The researching team used the magnetic signature of oceanic crust, fossil signatures from deep ocean sediments, and the position of the mantle ‘Hot Spot’ that resulted in the Hawaiian Islands. Daniel Woodworth, a Graduate Student at the Rice University who is also a Co-author of the study, explained the ‘True Polar Wander’ in the following words:

“The Hawaiian hot spot was fixed, relative to the spin axis, from about 48 million years ago to about 12 million years ago, but it was fixed at a latitude farther north than we find it today. By comparing the Hawaiian hot spot to the rest of the Earth, we can see that that shift in location was reflected in the rest of the Earth and is superimposed on the motion of tectonic plates. That tells us that the entire Earth moved, relative to the spin axis, which we interpret to be true polar wander.”

True Polar Wander. Credit: Wikipedia

Most of the Earth is made up of a solid rock that flows under intense heat and pressure. The rocky tectonic plates are present on top of the planet’s mantle. They bump and slip against each other at seismically active boundaries. According to a research conducted in 2017, the plumes of hot solid rock that rise from deep within the mantle, also known as Hot Spots, can be used as a global frame of reference for tracking the movement of these plates. Richard Gordon, the W.M. Keck Professor at the Department of Earth, Environmental, and Planetary Science and a Co-author of the study, explained that a True Polar Wander occurs when highly viscous bumps of mantle accumulate at any point away from the equator. He said,

“Imagine you have really, really cold syrup, and you’re putting it on hot pancakes. As you pour it, you temporarily have a little pile in the center, where it doesn’t instantly flatten out because of the viscosity of the cold syrup. We think the dense anomalies in the mantle are like that little temporary pile, only the viscosities are much higher in the lower mantle. Like the syrup, it will eventually deform, but it takes a really, really long time to do so.”

The study elaborated that humungous mantle anomalies can disturb the balance of the planet. Consequently, the equator shifts steadily to ensure that the excessive mass stays close to it. Despite that, the tilt of the Earth’s spin with respect to the Sun is not affected by this as the planet continues to spin once every 24 hours. Having said that, the change in equator alters the points on Earth where the spin axis emerges. In views of Woodworth, the data from Hawaii clearly indicates that True Polar Wander was the reason which caused the poles of Earth to start moving. Gordon agreed to him by saying,

“It was only about a 3-degree shift, but it had the effect of taking the mantle under the tropical Pacific and moving it to the south, and at the same time, it was shifting Greenland and parts of Europe and North America to the north. That may have triggered what we call the ice age.”

Gordon explained that, in such cases, not only the location of the Earth’s magnetic poles changes but the polarity of the magnetic field, created by the iron core of the planet, also flips itself several times. The magnetic signatures of rocks keep a record of these changes. Gordon mentioned that in addition to plate motion, the paleomagnetic record also showed signs of True Polar Wander. He claimed that the mantle of Earth continues to change all the time as new material constantly cycles in and out from tectonic plates. Both the researchers are now planning to extend their work from 12 million years ago to present as well as further into the past and we wish them all the best.

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